Extensible shaft for steering of vehicle

ABSTRACT

In a telescopic shaft for vehicle steering which is installed in a steering shaft of a vehicle and in which a male shaft ( 1 ) and a female shaft ( 2 ) are fitted to each other to be incapable of mutual rotation and capable of sliding, at least one set of torque transmitting members ( 7, 8 ) are interposed between at least one set of grooves ( 3, 4, 5, 6 ) formed on the outer peripheral surface of the male shaft and on the inner peripheral surface of the female shaft to be extended in the axial direction to face each other and at least one projection ( 40 ) formed to be axially concentric with at least one of the grooves ( 3, 4 ) extending in the axial direction on the outer peripheral surface of the male shaft is fitted in at least one of the grooves ( 5, 6 ) extended in the axial direction of the female shaft through a gap in the radial direction.

TECHNICAL FIELD

The present invention relates to a telescopic shaft for a steering of avehicle capable of achieving a stable sliding load and, at the sametime, of preventing a backlash without fail, thereby transmitting torquein a state of high rigidity.

BACKGROUND ART

FIG. 9 shows a conventional steering mechanism of a vehicle. In FIG. 9,reference symbols a and b denote telescopic shafts. In the telescopicshaft a, a male shaft and a female shaft are in spline fitting. Such atelescopic shaft a is required to have a function of absorbingdisplacement in the axial direction which is generated during running ofthe vehicle and of preventing such displacement or vibration from beingpropagated onto a steering wheel. Such a function is usually requiredwhen the vehicle body is in a sub-frame structure in which a portion cfor fixing an upper part of the steering mechanism and a frame e towhich a steering rack d is fixed are separately provided and bothmembers are fastened and fixed through an elastic member f such asrubber. There is also another case where a telescopic function isrequired for an operation, when fastening a steering shaft joint g to apinion shaft h, to temporarily contract the telescopic shaft to then fitand fasten it to the pinion shaft h. Further, the telescopic shaft b inan upper part of the steering mechanism also comprises a male shaft anda female shaft being in spline fitting. This telescopic shaft b isrequired to have the ability of extending and contracting in the axialdirection since it is required to have the function of moving thesteering wheel i to adjust the position thereof in order to obtain anoptimal position for the driver for driving the vehicle. In all thecases described above, the telescopic shaft is required to reducebacklash noise in a spline portion, to reduce the backlash feel on thesteering wheel, and to reduce a sliding resistance during a slidingmovement in the axial direction.

On that account, in FIGS. 1 through 6 of Japanese Patent ApplicationLaid-Open No. 2001-50293 (FIGS. 1 through 6 and FIG. 12), three sets ofspherical bodies or balls serving as torque transmitting members arefitted between the three sets of axial grooves formed on the outerperipheral surface of a male shaft and on the inner peripheral surfaceof a female shaft.

With this arrangement, backlash between the male shaft and the femaleshaft can be prevented when torque is not transmitted, and the maleshaft and the female shaft can slide in the axial direction with astable sliding load without backlash. On the other hand, the male shaftand the female shaft are capable of preventing backlash in the directionof rotation thereof so as to transmit torque in a state of high rigiditywhen the torque is transmitted.

In FIG. 12 of Japanese Patent Application Laid-Open No. 2001-50293(FIGS. 1 through 6 and FIG. 12), while the three sets of sphericalbodies or balls serving as the torque transmitting members areinterposed between the three sets of axial grooves formed on the outerperipheral surface of the male shaft and on the inner peripheral surfaceof the female shaft, another three axial grooves are formed at regularintervals between the three axial grooves of the female shaft in thecircumferential direction and furthermore, three projections are formedat regular intervals between the axial grooves of the male shaft in thecircumferential direction. These three projections are fitted in thelatter three axial grooves separately provided. However, there isallowed a predetermined gap, that is, play between the latter threeaxial grooves and the three projections in the radial direction.

With this arrangement, even when the spherical bodies or balls servingas the torque transmitting members are broken, the three projections arefitted in the latter axial grooves, whereby the male shaft and thefemale shaft can transmit torque and can discharge a fail safe function.

However, in Japanese Patent Application Laid-Open No. 2001-50293 (FIGS.1 through 6 and FIG. 12), the three sets of the spherical bodies orballs serving as the torque transmitting members, the three axialgrooves separately provided and the three projections are provided onthe same cross section (the same surface in the circumferentialdirection), so that the radial dimensions of the male shaft and thefemale shaft become great and the sizes thereof can not be reduced.

Also, in Japanese Patent Application Laid-Open No. 2001-50293 (FIGS. 1through 6 and FIG. 12), since the torque transmitting members consistonly of the spherical bodies or balls, there is required the sufficientnumber of the spherical bodies or balls for enduring the surfacepressure which is applied onto the spherical bodies or balls. As aresult, the axial grooves are elongated and the axial dimensions of themale shaft and the female shaft become great, so that the telescopicshaft can not be formed compact.

DISCLOSURE OF THE INVENTION

The present invention has been contrived taking such circumstances asdescribed above into consideration, and an object thereof is to providea telescopic shaft for a steering of a vehicle which is capable ofachieving a stable sliding load so as to prevent a backlash in adirection of rotation without fail, thereby transmitting torque in astate of high rigidity, and in which both the axial and radialdimensions thereof can be reduced to make the entire telescopic shaftcompact.

In order to achieve the above object, according to the presentinvention, there is provided an telescopic shaft for a vehicle steeringwhich is installed in a steering shaft of a vehicle and in which a maleshaft and a female shaft are fitted to each other to be incapable ofmutual rotation and capable of sliding, characterized in that:

at least one set of torque transmitting members are interposed betweenat least one set of grooves formed on the outer peripheral surface ofsaid male shaft and on the inner peripheral surface of said female shaftto be extended in the axial direction to face each other; and

at least one projection formed to be axially concentric with at leastone of said grooves extending in the axial direction on the outerperipheral surface of said male shaft is fitted in at least one of saidgrooves extended in the axial direction of said female shaft through agap in the radial direction.

According to the telescopic shaft for vehicle steering of the presentinvention, when the torque transmitting members slip off the male shaftor are broken for any reason, the projections of the male shaft arefitted in the grooves of the female shaft extended in the axialdirection, whereby the male shaft and the female shaft can transmit thetorque and can discharge the fail safe function.

In this case, since there is provided the gap in the radial directionbetween the grooves extended in the axial direction of the female shaftand the projections of the male shaft, the driver can feel a greatbacklash on the steering wheel and can sense any trouble of the steeringsystem.

Further, the projections of the male shaft are formed to be axiallyconcentric with the grooves extended in the axial direction of the maleshaft and are also axially concentric with the torque transmittingmembers, so that they can play the role of a stopper for restricting amovement of the torque transmitting members in the axial direction. As aresult, the possibility of slip-off of the torque transmitting membersis reduced so as to further enhance the fail safe function.

Further, the projections of the male shaft are formed to be axiallyconcentric with the axial grooves of the male shaft and are also axiallyconcentric with the torque transmitting members, so that the radialdimensions of the male shaft and the female shaft can be reduced to makethe entire telescopic shaft compact.

Also, in the telescopic shaft for vehicle steering according to thepresent invention, it is preferably possible to make the number of thesets of the torque transmitting members in the circumferential directionequal to the number of the projections in the circumferential direction.According to this preferable structure, the projections of the maleshaft is axially concentric with the torque transmitting members, asdescribed above and, moreover, can play the role of the stopper forrestricting the movement of the torque transmitting members in the axialdirection without fail since the number of the sets of the torquetransmitting members in the circumferential direction is set equal tothe number of the projections in the circumferential direction, wherebythe possibility of slip-off of the torque transmitting members can befurther reduced.

Further, in the telescopic shaft for vehicle steering according to thepresent invention, it is preferable that one end of the female shaft cancomprise an inward deformation portion which is inwardly deformed.According to this preferable structure, when the male shaft isrelatively moved in a direction of removing from the female shaft, theprojections of the male portion latch on to (interfere with) the inwarddeformation portion (e.g., a clamp portion) formed at the end of thefemale shaft. With this arrangement, the male shaft can not be separatedfrom the female shaft easily.

Further, in the telescopic shaft for vehicle steering according to thepresent invention, the torque transmitting members can preferablycomprise at least one set of spherical bodies and at least one set ofcolumnar bodies. According to this preferable structure, the torquetransmitting members comprise at least one set of spherical bodies andat least one set of columnar bodies, and have a slide mechanism forcausing both a rolling movement by means of the spherical bodies and asliding movement by means of the columnar bodies, so that the columnarbodies mainly receive a load when the torque is transmitted. As aresult, it is possible to reduce the size of the present structure,compared with the conventional one which is required to transmit torqueby point contact (the structure of transmitting torque only with balls),by reducing the size thereof in the axial direction.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical cross sectional view of a telescopic shaft for asteering of a vehicle according to one embodiment of the presentinvention;

FIG. 2 is a transverse cross sectional view of the telescopic shaft,taken along the line X-X in FIG. 1;

FIG. 3 is a transverse cross sectional view of the telescopic shaft,taken along the line Y-Y in FIG. 1;

FIG. 4 is a perspective view of an elastic member (leaf spring) coupledby a coupling portion;

FIG. 5 is a view of the telescopic shaft, seen along the arrow A in FIG.1;

FIG. 6 is a cross sectional view of the telescopic shaft, taken alongthe line Z-Z in FIG. 1;

FIG. 7 is a cross sectional view, taken along the line Z-Z in FIG. 1,according to a first variation of the embodiment of the presentinvention;

FIG. 8 is a cross sectional view, taken along the line Z-Z in FIG. 1,according to a second variation of the embodiment of the presentinvention; and

FIG. 9 is a side view of a conventional steering mechanism of a vehicle.

EMBODIMENTS OF THE INVENTION

A telescopic shaft for a vehicle according to an embodiment of thepresent invention will be described below with reference to drawings.

FIG. 1 is a longitudinal cross sectional view of a telescopic shaft fora steering of a vehicle according to one embodiment of the presentinvention, and FIG. 2 is a transverse cross sectional view of thetelescopic shaft, taken along the line X-X in FIG. 1.

As shown in FIG. 1, the telescopic shaft for a vehicle steering(hereinafter called the “telescopic shaft”) comprises a male shaft 1 anda female shaft 2 which are fitted to each other to be incapable ofmutual rotation and capable of sliding.

As shown in FIG. 2, three grooves 3 are provided on the outer peripheralsurface of the male shaft 1 at regular intervals of 120° in thecircumferential direction to be extended in the axial direction. On theouter peripheral surface of the male shaft 1, there are also provided atregular intervals of 120° in the circumferential direction threesubstantially arch-shaped grooves 4 which respectively arecircumferentially between the three grooves 3 extended in the axialdirection.

On the inner peripheral surface of the female shaft 2, there areprovided at regular intervals of 120° in the circumferential directionthree substantially arch-shaped grooves 5 which are extended in theaxial direction. On the inner peripheral surface of the female shaft 2,there are also provided three substantially arch-shaped grooves 6 whichare respectively circumferentially between the three grooves 5 extendedin the axial direction at regular intervals of 120° in thecircumferential direction.

The grooves 3 and 5 extended in the axial direction constitute threesets of first interposing sections for three sets of spherical bodies 7which will be described later, while the grooves 4 and 6 extended in theaxial direction constitute three sets of second interposing sections forthree sets of columnar bodies 8 which will be described later. The threesets of the grooves 3 and 5 extended in the axial direction (the firstinterposing sections) and the three sets of the grooves 4 and 6 (thesecond interposing sections) are provided alternately in thecircumferential direction at regular intervals of 60° in thecircumferential direction.

A first torque transmitting device is arranged such that, between thethree grooves 3 of the male shaft 1 extended in the axial direction andthe three grooves 5 of the female shaft 2 extended in the axialdirection, the three sets of the spherical bodies 7 serving as firsttorque transmitting members which are rotated when the male shaft 1 andthe female shaft 2 are moved in the axial direction relatively to eachother and are restrained by the leaf springs 9 when both shafts arerotated so as to transmit torque are interposed to be rotatable throughthree waveform elastic members (the leaf springs) 9 for applyingpreload.

A second torque transmitting device is arranged such that, between thethree grooves 4 of the male shaft 1 extended in the axial direction andthe three grooves 6 of the female shaft 2 extended in the axialdirection, the three sets of the columnar bodies 8 serving as secondtorque transmitting members which respectively allow an axial relativemovement of the male shaft 1 and the female shaft 2 so as to transmittorque during rotation are interposed to be slidable.

The leaf springs 9, while applying a preload to the spherical bodies 7and the columnar bodies 8 to the extent that no backlash is generatedwith respect to the female shaft 2 when the torque is not transmitted,are elastically deformed to retain the spherical bodies 7 between themale shaft 1 and the female shaft 2 in the circumferential directionwhen the torque is transmitted.

With the telescopic shaft having a structure as described above, sincethe spherical bodies 7 and the columnar bodies 8 are interposed betweenthe male shaft 1 and the female shaft 2 to preload the spherical bodies7 and the columnar bodies 8 to the extent that no backlash is generatedwith respect to the female shaft 2 by means of the leaf spring 9,backlash between the male shaft 1 and the female shaft 2 can beprevented without fail when the torque is not transmitted and the maleshaft 1 and the female shaft 2 can slide in the axial direction with astable sliding load with no backlash when the male shaft 1 and thefemale shaft 2 are moved in the axial direction relatively to eachother.

Note that, if a sliding surface employs only a pure sliding mechanism,as in the prior art, a preload for preventing backlash is obliged to beretained only a certain load. That is, since the sliding load isobtained by multiplying a coefficient of friction by a preload, if thepreload is increased in order to prevent backlash or enhancing therigidity of the telescopic shaft, the sliding load is increased, thusforming a vicious circle.

In this respect, since the present embodiment partially employs arolling mechanism, a preload can be raised without conspicuouslyincreasing a sliding load. With this arrangement, prevention of backlashand enhancement of the rigidity, which can not be achieved according tothe prior art, can be achieved without increasing the sliding load.

At torque transmission, the three sets of the lead springs 9 areelastically deformed to retain the three sets of the spherical bodies 7between the male shaft 1 and the female shaft 2 and, at the same time,the three sets of the columnar bodies 8 interposed between the maleshaft 1 and the female shaft 2 play the role of main transmitters of thetorque.

For instance, when torque is inputted from the male shaft 1, since apressure of the leaf springs 9 is applied at the early stage, there isgenerated no backlash and the leaf springs 9 produce a counter forceagainst the torque to transmit the torque. In this case, the torquetransmission is executed as a whole in a state that a torquetransmitting load among the male shaft 1, the leaf springs 9, thespherical bodies 7 and the female shaft 2 and a torque transmitting loadamong the male shaft 1, the columnar bodies 8 and the female shaft 2 arein balance.

When the torque is further increased, since a gap between the male shaft1 and the female shaft 2 in the direction of rotation through thecolumnar bodies 8 is set as smaller than that among the male shaft 1,the leaf springs 9, the spherical bodies 7 and the female shaft 2through the spherical bodies, the columnar bodies 8 receive the counterforce more strongly than the spherical bodies 7. As a result, thecolumnar bodies 8 mainly transmit the torque to the female shaft 2. Forthis reason, the backlash between the male shaft 1 and the female shaft2 in the direction of rotation can be prevented without fail and, at thesame time, the torque can be transmitted in a state of high rigidity.

Note that the spherical bodies 7 may be balls, and the columnar bodies 8may be needle rollers.

The needle rollers 8 are advantageous in various aspects since theyreceive the load with line contact and can keep the contact pressurelower than the balls 7 which receive the load with point contact. As aresult, this arrangement is superior in the following points to a casein which all of the arrays are in ball rolling structure.

-   -   The attenuating performance in the sliding portion is great,        compared with that in the ball rolling structure. As a result,        the vibration absorbing performance is high.    -   If the same torque is to be transmitted, the contact pressure        can be kept low in the needle roller structure. As a result, the        length in the axial direction can be reduced so as to use the        space effectively.    -   If the same torque is to be transmitted, the contact pressure        can be kept low in the needle roller structure. As a result,        there is no longer required an additional process for hardening        the surfaces of the axial grooves of the female shaft by thermal        treatment or the like.    -   The number of constituent parts can be reduced.    -   The assembling performance can be improved.    -   The assembling cost can be reduced.

As described above, the needle rollers 8 play the essential role fortorque transmission between the male shaft 1 and the female shaft 2, andare brought into sliding contact with the inner peripheral surface ofthe female shaft 2. This structure is superior to the conventionalspline fitting structure in the following respects.

-   -   The needle rollers are manufactured in mass production, and can        be manufactured at very low cost.    -   The needle rollers are polished after the thermal treatment, so        that they have high surface rigidity and excellent abrasion        fastness.    -   Since the needle rollers have been polished, they have fine        surface roughness and a low coefficient of friction in a sliding        movement. As a result, the sliding load can be kept low.    -   Since the length or the layout of the needle rollers can be        changed in accordance with the condition of use, the needle        rollers can answer various applications without changing the        design concept.    -   There is a case in which the coefficient of friction at sliding        is required to be further lowered, depending on the condition of        use. In such a case, the sliding characteristic can be changed        only by subjecting the needle rollers to the surface treatment.        As a result, the needle rollers can answer various applications        without changing the design concept.    -   Since needle rollers having different outer diameters by several        microns can be manufactured at low cost, the gap among the male        shaft, the needle rollers, and the female shaft can be minimized        by selecting a diameter of the needle rollers. As a result, the        rigidity of the shaft in the twist direction can be improved        easily.

On the other hand, the present structure is superior since partiallyemploying the balls, to a structure in which all arrays are constitutedby needle rollers and all arrays are sliding, in the following respects.

-   -   Since a frictional resistance is low, the sliding load can be        kept low.    -   The preload can be raised, so that prevention of backlash and        high rigidity over a long period of time can be attained at the        same time.

FIG. 3 is a transverse cross sectional view taken along the line Y-Y inFIG. 1, FIG. 4 is a perspective view of the leaf spring which serves asan elastic member coupled by a coupling portion, and FIG. 5 is a viewseen along the arrow A in FIG. 1.

As shown in FIG. 1, a small diameter portion 1 a is formed at one end ofthe male shaft 1. This small diameter portion 1 a is provided with astopper plate 10 for restricting an axial movement of the needle roller8. This stopper plate 10 is comprised of an elastic member 11 forapplying preload in the axial direction and one set of flat plates 12,13 for sandwiching this elastic member 11 therebetween.

That is, in the present embodiment, the stopper plate 10 is fitted inthe small diameter portion 1 a at the flat plate 13, the elastic member11 for axial preload and the flat plate 12 in this order, and is fixedto the small diameter portion 1 a firmly.

In the present embodiment, a circumferential groove 31 is formed in thesmall diameter portion 1 a of the male shaft 1, and a stop ring 32 isfitted in this circumferential groove 31. With this arrangement, thestopper plate 10 is fixed in the axial direction. Note that means forfixing the stopper plate 10 is not limited to the stop ring 32, but maybe caulking (or clinching), threadably engaging means, push nut, or thelike.

With this structure, the stopper plate 10 brings the flat plate 13 intopressure contact with the needle rollers 8, so as to apply appropriatepreload to the needle rollers 8 in such a manner that they are not movedin the axial direction by means of the elastic member 11 for axialpreload.

The elastic member 11 for axial preload is formed of rubber, resin, or aleaf spring made of a steel plate. The elastic member 11 for axialpreload and the flat plates 12 and 13 may be formed separately, but arepreferably formed as a unitary structure, in order to attain easierassembling.

For instance, when the elastic member 11 is formed of rubber, if theflat plates 12 and 13 are formed by vulcanizing process, or the like,both members can be integrally formed to resultantly provide a productwhich can be assembled easily and manufactured at low cost.

Also, when the elastic member 11 is formed of resin, the elastic member11 may be formed in a wave shape and can be formed integrally with theflat plates 12 and 13 as a unitary structure. As a result, the samemerits can be obtained.

Furthermore, the flat plates 12 and 13 may be formed of a steel plate orresin, or by coating resin film on a steel plate.

The axial grooves 3 and 4 of the male shaft 1 are formed substantiallyperpendicularly to the axial direction, and have surfaces 14 and 15which are right-angled to the axial direction and in contact with theballs 7 or the needle rollers 8.

As described above, one end of the needle roller 8 is prevented frommoving in the axial direction by the stopper plate 10 which is providedin the small diameter portion 1 a of the male shaft 1. On the otherhand, the other end of the needle roller 8 is brought into contact withthe axially right-angled surface 15 to be prevented from moving in theaxial direction.

The stopper plate 10 brings the flat plate 13 into contact with theneedle rollers 8, and appropriately preload the needle rollers 8 in sucha manner that they are not moved in the axial direction by means of theelastic member 11 for axial preload.

As a result, the needle rollers 8 can be properly preloaded and fixedwithout gap in the axial direction, and when the male shaft 1 and thefemale shaft 2 slide relatively to each other, unpleasant abnormal soundsuch as rapping sound can be prevented without fail.

The grooves 3 and 4 extended in the axial direction of the male shaft 1,have the axially right-angled surfaces 14 and 15 which are substantiallyperpendicular to the axial direction, and are in contact with the balls7 and the needle rollers 8, so that the axial movement of the balls 7 orthe needle rollers 8 can be restricted by the axially right-angledsurface 15 and no other member is required to be provided separately forthis purpose. As a result, the number of the constituent parts can bedecreased to reduce the manufacturing cost and, moreover, the weight andthe size of the whole shaft can be reduced since such a separate memberis not employed.

Next, in the present embodiment, as shown in FIGS. 1, 3 and 4, the threeleaf springs 9 for preloading the three sets of the balls 7 areintegrally coupled by a ring-shaped coupling portion 20.

That is, as shown in FIG. 1, the small diameter portion 1 a at one endof the male shaft 1 is formed with an annular surface 21 as a stepthereof. The ring-shaped coupling portion 20 is fitted in the smalldiameter portion 1 a, and the ring-shaped coupling portion 20 isprovided along the annular surface 21 of the step.

The annular surface 21 of the step may take any form, etc., so long asit is an axially annular surface facing the axial direction of the maleshaft 1.

The ring-shaped coupling portion 20 is coupled to end portions of thethree leaf springs 9 in the axial direction at three positions on theperiphery thereof. That is, as shown in FIG. 4, the ring-shaped couplingportion 20 is formed integrally with the three leaf springs 9 extendedin the axial direction as a unitary structure.

As a result, though in this structure the balls 7 and the needle rollers8 are combined with each other, the actual number of the constituentparts can be reduced from three to one by integrally forming three leafsprings 9 which respectively forms rolling surfaces, whereby the numberof the constituent parts can be reduced, the assembling performance canbe enhanced and the assembling time can be shortened, thereby reducingthe manufacturing cost. It is possible to omit the coupling portion 20and form the three leaf springs 9 as respective separate members.

Since the ring-shaped coupling portion 20 is not like a conventionalarch-shaped coupling portion which is extended in the circumferentialdirection, the female shaft 2 is not enlarged in the radial direction sothat the size of the shaft can be reduced.

Further, the small diameter portion 1 a which is formed at the end ofthe male shaft 1 is thrust through the ring-shaped coupling portion 20.Accordingly, when the three leaf springs 9 are assembled, the smalldiameter portion 1 a at the end of the male shaft 1 plays the role of aguide in this assembling by thrusting through the ring-shaped couplingportion 20, whereby the assembling work can be performed easily and theassembling time can be reduced, thereby reducing the manufacturing cost.

Further, the ring-shaped coupling portion 20 is disposed in an axial gap1 between the flat plate 13 of the stopper plate 10 and the annularsurface 21 of the step. This axial gap 1 has a size of, for example,about 0.3 mm to 2.0 mm.

Due to the presence of this axial gap 1, the ring-shaped couplingportion 20 does not restrain the movement of the three leaf springs 9when these leaf springs 9 are deformed upon input of the torque.

Further, as shown in FIGS. 3 and 4, each leaf spring 9 has a crosssection which is formed as a straight line which is formed substantiallyin parallel to the form of the axial groove 3 of the male shaft 1, andis comprised of a flat bottom portion 9 a at the center thereof, firstinclined side surfaces 9 b, 9 b which are extended as gradually widenedoutward from both ends in a direction perpendicular to the axialdirection with respect to this flat bottom portion 9 a, and secondinclined side surfaces 9 c, 9 c which are folded back outward on theoutermost diameter sides of these first inclined side surfaces to beextended substantially in parallel to the first inclined side surfaces 9b, 9 b. The peripheral part of the ring-shaped coupling portion 20 iscoupled to the flat bottom portion 9 a at the center of each leaf spring9. The flat bottom portion 9 a of each leaf spring 9 is brought intopressure contact with a flat bottom portion 3 a of the groove 3 whilethe second side surfaces 9 c, 9 c are brought into pressure contact withflat side surfaces 3 b, 3 b of the groove 3, whereby the balls 7 and theneedle roller 8 are pressed against a side surface of the groove 5 ofthe female shaft 2 by means of the first side surfaces 9 a, 9 a.

Further, the small diameter portion 1 a formed at the end of the maleshaft 1 is inserted through the ring-shaped coupling portion 20. Aradial gap is formed between the small diameter portion 1 a of the maleshaft 1 and the ring-shaped coupling portion 20. This radial gap has asize of, for example, 0.2 mm to 1.0 mm. Like the axial gap describedabove, due to the presence of this radial gap, it is arranged such thatthe ring-shaped coupling portion 20 does not restrain the movement ofthese leaf springs 9 even when the three leaf springs 9 are deformedupon input of the torque.

Next, as shown in FIGS. 1 and 6, in the present embodiment, sixsubstantially arch-shaped projections 40 which are formed axiallyconcentrically with the six grooves 3 and 4 which are extended in theaxial direction on the outer peripheral surface of the male shaft 1 areopposite to the six grooves 5 and 6 of the female shaft 2 extended inthe axial direction through a gap in the radial direction.

As a result, when the ball 7 or the needle roller 8 slips off the maleshaft 1 or is broken for any reason, the projections 40 of the maleshaft 1 are fitted in the grooves 5 and 6 of the female shaft 2 extendedin the axial direction, whereby the male shaft 1 and the female shaft 2can transmit torque and can discharge the fail safe function.

As shown in FIG. 6, since there is formed a gap between the grooves 5and 6 extended in the axial direction of the female shaft 2 and theprojections 40 of the male shaft 1, the driver can feel great backlashon the steering wheel and can sense any trouble of the steering system.

Further, as shown in FIG. 1, the projections 40 of the male shaft 1 areformed concentrically with the grooves 3 and 4 of the male shaft 1extended in the axial direction and also concentrically with the balls 7and the needle rollers 8, so as to play the role of stoppers forrestricting the axial movement of the balls 7 and the needle rollers 8.Thus, the possibility of slip-off of the ball 7 or the needle roller 8is reduced to further enhance the fail safe function.

Further, the projections 40 of the male shaft 1 are formedconcentrically with the grooves 3 and 4 of the male shaft extended inthe axial direction and concentrically also with the balls 7 or theneedle rollers 8, so that the radial dimensions of the male shaft 1 andthe female shaft 2 can be decreased so as to reduce the sizes thereof.

Also, the projections 40 of the male shaft 1 are formed concentricallywith the balls 7 and the needle rollers 8 in the axial direction asdescribed above, and moreover, the number of sets of the balls 7 or theneedle rollers 8 in the circumferential direction is set to be equal tothe number of projections 40 in the circumferential direction, so thatthe projections 40 can play the role of the stopper for restricting theaxial movement of the balls 7 or the needle rollers 8 without fail. As aresult, the possibility of slip-off of the balls 7 and the needlerollers 8 is further reduced to further enhance the fail safe function.

Further, an end of the female shaft 2 is provided with an inwarddeformation portion 41 which is deformed inward. Specifically, thisinward deformation portion 41 is formed by caulking or plasticallydeforming the end of the female shaft 2.

With this arrangement, when the male shaft 1 is moved in a direction ofslipping off the female shaft 2, the projection 40 of the male shaft 1latches on to (interfered with) the inward deformation portion 41 (forexample, the caulked or clinched portion) which is formed at the end ofthe female shaft 2. Thus, it is arranged such that the male shaft 1 isnot easily separated from the female shaft 2.

Next, FIG. 7 is a cross sectional view, taken along the line Z-Z in FIG.1, according to a first variation of the embodiment of the presentinvention.

In this variation, the three substantially arch-shaped projections 40which are formed concentrically with the three grooves 3 formed on theouter peripheral surface of the male shaft 1 to be extended in the axialdirection are opposite to the three grooves 5 of the female shaft 2extended in the axial direction through a gap existing therebetween inthe radial direction.

That is, the three projections 40 are provided only on the rear side ofthe vehicle of the three sets of the balls 7.

Accordingly, when the balls 7 slip off the male shaft 1 or are brokenfor any reason, the projections 40 of the male shaft 1 are fitted in thegrooves 5 of the female shaft 2 extended in the axial direction, wherebythe male shaft 1 and the female shaft 2 can transmit torque and candischarge the fail safe function.

In this case, as shown in FIG. 7, since there is formed the gap betweenthe grooves 5 of the female shaft 2 extended in the axial direction andthe projections 40 of the male shaft 1, the driver can feel greatbacklash on the steering wheel and can sense any trouble of the steeringsystem.

Further, as shown in FIG. 1, the projections 40 of the male shaft 1 areformed axially concentrically with the grooves 3 of the male shaft 1extended in the axial direction and also concentrically with the balls 7in the axial direction, so as to play the role of the stoppers forrestricting the axial movement of the balls 7. Thus, the possibility ofslip-off of the balls 7 is reduced to further enhance the fail safefunction.

Further, the projections 40 of the male shaft 1 are formedconcentrically with the grooves 3 of the male shaft 1 extended in theaxial direction and also concentrically with the balls 7 in the axialdirection, so that the radial dimensions of the male shaft 1 and thefemale shaft 2 can be decreased so as to reduce the sizes thereof.

Also, the projections 40 of the male shaft 1 are formed concentricallywith the balls 7 in the axial direction as described above, andmoreover, the number of the sets of the balls 7 in the circumferentialdirection is set to be equal to the number of the projections 40 in thecircumferential direction, so that the projections 40 can play the roleof the stoppers for restricting the axial movement of the balls 7without fail. As a result, the possibility of slip-off of the ball 7 isfurther reduced.

Next, FIG. 8 is a cross sectional view, taken along the line Z-Z in FIG.1, according to a second variation of the embodiment of the presentinvention.

In the second variation, the three substantially arch-shaped projections40 which are formed concentrically with the three grooves 4 formed onthe outer peripheral surface of the male shaft 1 to be extended in theaxial direction are opposite to the three grooves 6 of the female shaft2 extended in the axial direction through a radial gap existingtherebetween.

That is, the three projections 40 are provided only on the rear side ofthe vehicle of the three sets of the needle rollers 8.

Accordingly, when the needle rollers 8 slip off the male shaft 1 or arebroken for any reason, the projections 40 of the male shaft 1 are fittedin the grooves 6 of the female shaft 2 extended in the axial direction,whereby the male shaft 1 and the female shaft 2 can transmit torque andcan discharge the fail safe function.

Also, in this case, as shown in FIG. 8, since there is formed the gapbetween the grooves 6 extended in the axial direction and theprojections 40, the driver can feel great backlash on the steering wheeland can sense any trouble of the steering system.

Further, as shown in FIG. 1, the projections 40 of the male shaft 1 areformed concentrically in the axial direction with the grooves 4 of themale shaft extended in the axial direction and also concentrically withthe needle rollers 8 in the axial direction, so as to play the role ofthe stoppers for restricting the axial movement of the needle rollers 8.Thus, the possibility of slip-off of the needle rollers 8 is reduced tofurther enhance the fail safe function.

Further, the projections 40 of the male shaft 1 are formedconcentrically in the axial direction with the grooves 4 of the maleshaft 1 extended in the axial direction and also concentrically with theneedle rollers 8 in the axial direction, so that the radial dimensionsof the male shaft 1 and the female shaft 2 can be decreased so as toreduce the sizes thereof.

Also, the projections 40 of the male shaft 1 are formed concentricallywith the needle rollers 8 in the axial direction, as described above,and moreover, the number of sets of the needle rollers 8 in thecircumferential direction is set to be equal to the number ofprojections 40 in the circumferential direction, so that the projections40 can play the role of the stoppers for restricting the axial movementof the needle rollers 8 without fail. As a result, the possibility ofslip-off of the ball 7 is further reduced.

Note that the present invention is not limited to the embodimentsdescribed above, but can be altered in various manners.

As described above, according to the present invention, the projectionswhich are formed concentrically in the axial direction with the axialgrooves formed on the outer peripheral surface of the male shaft arefitted in the axial grooves of the female shaft through the gap in theradial direction exiting therebetween.

As a result, when the torque transmitting members slip off the maleshaft or are broken for any reason, the projections of the male shaftare fitted in the axial grooves of the female shaft, whereby the maleshaft and the female shaft can transmit torque and can discharge thefail safe function.

Also, since there is formed the gap between the axial grooves and theprojections in this case, the driver can feel great backlash on thesteering wheel and can sense any trouble of the steering system.

Further, the projections of the male shaft are formed concentrically inthe axial direction with the axial grooves of the male shaft and alsoconcentrically with the torque transmitting members in the axialdirection, so as to play the role of the stoppers for restricting theaxial movement of the torque transmitting members. Thus, the possibilityof slip-off of the torque transmitting members is reduced to furtherenhance the fail safe function.

Further, the projections of the male shaft are formed concentrically inthe axial direction with the axial grooves of the male shaft and alsoconcentrically with the torque transmitting members in the axialdirection, so that the radial dimensions of the male shaft and thefemale shaft can be decreased so as to reduce the sizes thereof.

1. A telescopic shaft for vehicle steering which is installed in asteering shaft of a vehicle and in which a male shaft and a female shaftare fitted to each other to be capable of transmitting torquetherebetween and moving in an axial direction, characterized in that: atleast one first pair of axially extending grooves is formed respectivelyon an outer peripheral surface of said male shaft and an innerperipheral surface of said female shaft so as to face each other with atleast one spherical body, radially biased by a spring, interposedtherebetween; and for at least one said first pair of grooves, acorresponding projection is formed on the outer peripheral surface ofsaid male shaft so as to be axially juxtaposed to the correspondinggroove formed on the outer peripheral surface of said male shaft and soas to be fitted, through a gap, in the corresponding groove formed onthe inner peripheral surface of said female shaft.
 2. A telescopic shaftfor vehicle steering according to claim 1, wherein at least one secondpair of axially extending grooves is formed respectively on the outerperipheral surface of said male shaft and an inner peripheral surface ofsaid female shaft so as to face each other with at least one columnarbody being interposed therebetween, said second pair of grooves beingadjacent in a circumferential direction to at least one said first pairof grooves.
 3. A telescopic shaft for vehicle steering according toclaim 1, wherein one said projection is provided for each said firstpair of grooves.
 4. A telescopic shaft for vehicle steering according toclaim 1, wherein said female shaft comprises at an end thereof adeformation portion which is deformed inwardly.
 5. A telescopic shaftfor vehicle steering which is installed in a steering shaft of a vehicleand in which a male shaft and a female shaft are fitted to each other tobe capable of transmitting torque therebetween and moving in an axialdirection, characterized in that: at least one first pair of axiallyextending grooves is formed respectively on an outer peripheral surfaceof said male shaft and an inner peripheral surface of said female shaftso as to face each other with at least one torque transmitting memberinterposed therebetween, said one torque transmitting member, for atleast one said first pair of grooves, being a spherical body biasedradially by a spring; and for at least one said first pair of grooves, acorresponding projection is formed on the outer peripheral surface ofsaid male shaft so as to be axially juxtaposed to the correspondinggroove formed on the outer peripheral surface of said male shaft and soas to be fitted, through a gap, in the corresponding groove formed onthe inner peripheral surface of said female shaft.
 6. A telescopic shaftfor vehicle steering according to claim 5, wherein one said projectionis provided for each said first pair of grooves.
 7. A telescopic shaftfor vehicle steering according to claim 5, wherein said female shaftcomprises at an end thereof a deformation portion which is deformedinwardly.